Such a heat exchanger, which is useful especially as a condenser in an air conditioning installation for a motor vehicle, is described in the specification of published European patent application No. EP 0 198 581A. In this known heat exchanger, the tubular wall has a convexity in each of its zones lying between two consecutive apertures for receiving the heat exchanger fluid flow tubes. This convexity extends outwardly, both in the longitudinal direction and in the transverse or circumferential direction. This transverse convexity makes it difficult to ensure that the tubular wall is immobilised against rotation about its axis during its assembly to the flow tubes of the heat exchanger. There is thus a danger that it will pivot under the force exerted by the tubes as they are introduced into the apertures, thus leading to wrong positioning of the fluid manifold with respect to the tubes, or even preventing their assembly from being carried out at all.